1. Field of the Invention
The present invention is directed to a system and method for providing a smart antenna system in which an antenna array can attach to an external port of a transceiver without any modification of the transceiver.
2. Description of the Related Art
In the past, companies had turned to wireless local area networks (WLANs) only to support low data intensive applications such as inventory management in warehouses and retail price marking in stores. For these applications, even though wireless network interface cards (NIC) are very costly, the improved efficiency derived from going wireless was worth the investment. The high price and low data rates, however, limited the usefulness and penetration of WLANs for general applications.
With the introduction of inexpensive, high-performance 11 M bit/sec products based on the IEEE 802.11b (Wi-Fi) standard, acceptance of WLANs for home, Small Office Home Office (SOHO) and enterprise applications has been increasing significantly. Home-based LANs have accounted for most of the initial market growth. The use of broadband connections and multiple PCs in the home has spurred home users to employ easy to install WLANs to share the broadband connection and network their computers. Wi-Fi adoption is quickly reaching mainstream levels as a communications technology across the enterprise, service providers and home.
Growth in enterprise WLAN deployments has also begun to accelerate. It has been found that wireless networks contribute to a better working environment and higher productivity for employees while bringing down the costs of networking.
Recently, WLANs have begun to get support from traditional wireless and wireline service providers. Public telecom carriers view Wi-Fi 802.11 connectivity as a new type of “data subscription” service that eventually will give users access to different types of wireless networks, either local or wide area, depending on what is available in a given location. Companies such Sprint, Verizon Wireless and SBC Communications have unveiled their Wi-Fi rollout plans. SBC also announced it was rolling out Wi-Fi in public hot spots to support its bundled DSL broadband offering. Traditional wireless carriers are adding Wi-Fi to their product offerings.
WLAN technology is also becoming standard equipment in portable computers. Notebook computer manufacturers such as IBM, Dell, HP/Compaq and Toshiba are building Wi-Fi into their systems, as notebook computers become the systems of choice for corporate users.
This explosion in growth comes despite the fact that today's Wi-Fi semiconductor chips have many shortcomings. The key limitation is that end-users do not experience the same quality of service. End-users can be too far away from an access point, behind a wall, in a “dead spot”, or working off a laptop. In addition, WLANs fall short of expected range when actually deployed. Even though a vendor's specifications may state that the wireless has a range of 300 feet, for example, obstacles such as walls, desks and filing cabinets can significantly decrease the range and coverage uniformity in some directions.
Smart antennas can significantly improve the performance of wireless systems by adaptively weighting and combining the signals received by multiple antennas. These antennas can increase receive signal gain, mitigate multipath fading, suppress interference, and increase throughput. Using smart antennas on transmission can also improve performance at the desired user as well. Conventional implementation of smart antennas typically required major modification to the RF, baseband, and MAC portions of the transceiver, which is a time consuming and costly process. Many wireless systems have an external antenna port for the transceiver. However, this port is generally used to attach a fixed, higher gain antenna.
The three physical layer standards for 802.11 are 802.11b, 802.11g, and 802.11a. 802.11b uses a single carrier with data rates of 1, 2, 5.5, and 11 Mbps, and operates in the 2.4 GHz unlicensed band. At the beginning of each data packet, there is a preamble, the first 20 microseconds of which are available for antenna selection purposes (as used by many 802.11 receivers). 802.11g and 802.11a use OFDM modulation, with data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, operating in the 2.4 and 5.5 GHz unlicensed bands, respectively. At the beginning of each data packet, the preamble only contains about 2 microseconds for antenna selection purposes. All three techniques use time-division-duplexing (TDD), that is, the same frequency is used for transmission as for reception.
In consideration of the incorporation of smart antennas into 802.11 systems, one method is to completely redesign the 802.11 transceiver with smart antenna processing as an integral part. This method allows for the optimal performance improvement with M antennas, as well as for design optimization. However, it has the following significant disadvantages. First, it requires a substantial redesign effort by every chip manufacturer without the gains being completely verified until the chip is completed. Second, it results in an across the board increase in the cost of the 802.11 chipset for smart antenna gains that may not be appreciated by all users. Given that the current market is very price sensitive, any undervalued increase in cost will definitely result in lost sales by consumers who may not understand or know if they need the gains of smart antennas, and purchase on price alone. One way for chip vendors to avoid this risk is to create two versions of their chips: one with and one without smart antenna functionality. However, if the chip manufacturers make two versions of their chips without at least a doubling of volume, they risk the price advantage that comes through volume. Finally, consumers that purchased WLANs without smart antennas, and then found that they needed them, would have to completely replace their access points, client cards or both.
It is desirable to provide a smart external antenna module that provides an antenna array that can attach to an external port of a transceiver without any modification of the transceiver to provide improved performance with low manufacturing costs.